This invention relates to an ultrasonic diagnosis apparatus, and more particularly to a novel technique which is effectively applicable to an ultrasonic diagnosis apparatus which accurately measures and displays the distribution of the moving speed of an internal part of a living body, together with the moving speed dispersion and reflected-wave intensity.
A prior art, ultrasonic diagnosis apparatus which can measure the moving speed of an internal moving part of a living body and display the moving speed distribution in a two-dimensional mode is disclosed in, for example, Japanese Unexamined Patent Publication No. 58-188433 (JP-A No. 58-188433) laid open on Nov. 2, 1983.
The invention of the cited patent publication employs a usual transmission/reception scheme such that the direction of reception of an ultrasonic beam transmitted from an ultrasonic probe is the same as the direction of transmission. By the use of such a scheme, the speed distribution of an internal moving part of a living body scanned by the ultrasonic beam is measured, and the point scanned by the ultrasonic beam is successively displaced very slightly to display a two-dimensional image of the speed distribution of the internal moving part of the living body on a display unit.
However, in order to improve the accuracy of measurement of the moving speed of the internal moving part of the living body, a multiplicity of transmission and reception approaches had to be made in the same direction of the living body. Further, due to a limited image completion time attributable to the velocity of the ultrasonic beam, the frame rate of the image displayed in real time has not necessarily been satisfactory. Describing more concretely, a length of time of about 1.3 .mu.sec is required for an ultrasonic beam to shuttle a distance of 1 mm in a living body. Therefore, a length of time of, for example, about 1.3.times.180 .mu.sec is required for the ultrasonic wave to shuttle a distance of 180 mm. It is noted that when the so-called ultrasonic Doppler effect is utilized to detect the speed and speed dispersion of a blood flow to acquire data required for diagnosis, the ultrasonic beam must be transmitted many times. Suppose, for example, that the ultrasonic beam is transmitted ten times in one direction for inspecting an object which is located at a depth of 180 mm. In such a case, a length of time of about 1.3.times.180.times.10 .mu.sec is required. Suppose further that 50 scanning lines are required to complete one screen image. Then, an image completion time as long as about 1.3.times.180.times.10.times.50 .mu.sec is required.
Further, there is a low-speed internal moving part such as, for example, the wall of the heart. The moving speed of such a moving part is considerably low compared with that of the blood flow which is the object of measurement, and the intensity of reflected wave from such a low-speed moving part is very high compared with that from the blood flow. Thus, this low-speed moving part obstructs accurate measurement of the moving speed of the blood flow. Signal components reflected from such a low-speed moving part or a stationary part have frequencies close to the transmission repetition frequency. Therefore, the aforementioned known method employing a one-channel single-cancel complex signal canceller has been defective in that the signal components reflected from such a low-speed moving part or a stationary part cannot be sufficiently removed.
A scanning region of about 55.degree., a diagnosis depth of about 14 cm and the number of scanning lines of 32 are an example of display in a prior art ultrasonic diagnosis apparatus capable of displaying a two-dimensional image of the distribution of the moving speed of an internal moving part of a living body. The image actually displayed on the display unit has a coarse density of scanning lines, i.e. a pattern similar to that shown by the solid-line portion A on the right-hand half of FIG. 9. In the case of an image displaying the speed distribution of an internal moving part located at a large depth, the displayed image has a pattern similar to comb teeth. Therefore, the prior art apparatus has been defective in the density of scanning lines is low or the resolution is poor.